The present invention relates generally to pencil sharpeners, and more specifically to a pencil sharpener that includes an automatic stop (i.e., shut off) feature.
Manually operated and electrically powered pencil sharpeners are commonplace in modern society. When a pencil is inserted through a pencil-receiving opening of a pencil sharpener's housing, the pencil enters a sharpening assembly which cuts an outer layer of wood to expose and sharpen an inner core of lead or graphite. Some manual pencil sharpeners include a selector guide. The selector guide typically includes several openings sized to correspond to pencils of different thicknesses, for example, a standard adult size or a larger diameter child size pencil. The various openings of the selector guide are positionable in alignment with the pencil-receiving opening. The selector guide maintains proper alignment of the pencil with the sharpening assembly during the sharpening process.
Various configurations of electrically powered pencil sharpeners are known. A common electric pencil sharpener has a sharpening assembly that includes a rotary means rotatable by a motor and cutter means operatively carried by the rotary means so as to rotate in a direction opposite to a rotational direction of the rotary means. While such pencil sharpeners are easy to use, they can quickly cause excess wear and waste of the pencil, i.e., by oversharpening. This problem is particularly acute with children lacking experience, judgment, and/or adequate hand/eye coordination. Accordingly, some electric pencil sharpeners include a self-governing sharpening assembly having a mechanism for preventing excess oversharpening of a pencil.
Many sharpeners utilize pencil tip stops that give the user feedback in the form of increased resistance and a change in pitch of the motor. However, these stops are sometimes difficult to sense, especially for children. Other pencil sharpeners on the market include a more advanced feature known as a “fly-away” cutter that mechanically disengages the cutter when the sharpened pencil tip contacts a plate at the very end of the pencil-receiving bore. This type of mechanism prevents over-sharpening and provides a more distinct “stop” and change in pitch of the motor. However, a significant disadvantage of this system is that it is not well understood by many users of such systems. Users sometimes attribute the disengaged cutters to a malfunction in the sharpener since the motor remains running even after sharpening has ceased. Additionally, because the motor keeps running the sharpener continues to produce unwanted noise, which is problematic in the office and classroom environments. Other pencil sharpeners include visual indicators to inform the user that sharpening process is complete. A common implementation is to place an electrical switch where it can be actuated from a mechanical pencil-tip contact plate. This type of design requires precise mechanical tolerances for effective operation. If the switch is actuated too early, the indicator will illuminate before sharpening is complete and if the switch mechanism is placed too far back in the pencil bore, it may not function at all.
Considering the above-listed complexities and problems with commercially available pencil sharpeners, there is an ongoing need for an electric pencil sharpener that prevents oversharpening of pencils, but that does so in a consistent and reliable manner and that does not require overly complex devices or difficult to understand systems of operation.